1. Field of the Invention
The invention relates to video processing, and in particular to video processing method and apparatus employing a conventional analog user interface to control a digital video decoder.
2. Description of the Related Art
FIG. 1 shows block functions of a conventional analog video decoder, in which analog video signal 101 is input through several inputs into analog video decoder 100, in which video multiplexer 102 selects and forwards the video signal 101 to analog signal processor 103 and, based upon the analog values of external variable resistors 104, analog signal processor 103 decodes and processes video signal 101 for output. In real world video applications, each variable resistor 104 is an analog user interface, for example, generating an analog control signal to fine tune the image quality of a display and having a corresponding knob on the display.
As complementary metal oxide semiconductor (CMOS) process progresses, analog video decoders, formerly implemented by bipolar transistors, have evolved into digital function. FIG. 2 shows a circuit of a conventional digital video decoder. Analog video signal 201, through several interfaces, is sent to digital video decoder 200, in which each video multiplexer 202 selects one of the inputs and forwards the video signal thereof to an analog-to-digital converter (ADC) 203. Analog video signal 201 is converted by ADC 203 to digital video signal 207 and sent to digital signal processor (DSP) 204. Based on the setup values in register set 205, DSP 204 processes digital video signal 207 to output corresponding digital signal 209. The control of digital video decoder 200 is provided by a digital interface 205, allowing access to content of register set 205 by way of protocols such as I2C or SPI.
The system client of video decoders, while wanting to gain the benefits of digital video decoders, may desire to keep the case of a display intact, with knobs and variable resistors unchanged. An ADC and micro control unit (MCU) may be added, accordingly.
FIG. 3 shows a combination circuit with a digital video processor, an external ADC, and an external MCU. In FIG. 3, external ADC 301 and external MCU 303 cooperate with digital video processor 300. Via external ADC 301, the setup values of variable resistors 302 are converted by ADC 301 from analog form into digital form. MCU 303 generates parameters corresponding to the digitalized setup values to accordingly control digital video processor 300. As mentioned, via a protocol between MCU 303 and digital video processor 300, MCU 303 can access or change the content in the register set of digital video processor 300, such that image quality of a corresponding display is controlled by variable resistors 302.
According to the foregoing description, control of a digital video processor through an analog interface entails addition of an ADC and MCU as a buffer between interfaces. Such a configuration increases costs due to the additional ADC and MCU. External ADC and MCU require more complicated storage management and more area on a printed circuit board (PCB), reducing yield. Even if the additional ADC and MCU are internally implemented, i.e., embedded in a digital video processor, the additional ADC occupies considerable area and complicates the design of the integrated digital video processor.